pretrain_bert.py

# coding=utf-8
# Copyright (c) 2019, NVIDIA CORPORATION.  All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
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"""Pretrain BERT"""

import torch
import torch.nn.functional as F

from configure_data import configure_data
from megatron import mpu
from megatron.model import BertModel
from megatron.utils import print_rank_0
from megatron.utils import vocab_size_with_padding
from megatron.training import run


def model_provider(args):
    """Build the model."""

    print_rank_0('building BERT model ...')

    model = BertModel(
        num_layers=args.num_layers,
        vocab_size=args.vocab_size,
        hidden_size=args.hidden_size,
        num_attention_heads=args.num_attention_heads,
        embedding_dropout_prob=args.hidden_dropout,
        attention_dropout_prob=args.attention_dropout,
        output_dropout_prob=args.hidden_dropout,
        max_sequence_length=args.max_position_embeddings,
        checkpoint_activations=args.checkpoint_activations,
        checkpoint_num_layers=args.checkpoint_num_layers,
        add_binary_head=True,
        layernorm_epsilon=args.layernorm_epsilon,
        num_tokentypes=args.tokentype_size,
        parallel_output=True)

    return model


def get_batch(data_iterator, timers):

    # Items and their type.
    keys = ['text', 'types', 'is_random', 'mask', 'mask_labels', 'pad_mask']
    datatype = torch.int64

    # Broadcast data.
    timers('data loader').start()
    if data_iterator is not None:
        data = next(data_iterator)
    else:
        data = None
    timers('data loader').stop()
    data_b = mpu.broadcast_data(keys, data, datatype)

    # Unpack.
    tokens = data_b['text'].long()
    types = data_b['types'].long()
    next_sentence = data_b['is_random'].long()
    loss_mask = data_b['mask'].float()
    lm_labels = data_b['mask_labels'].long()
    padding_mask = data_b['pad_mask'].byte()

    return tokens, types, next_sentence, loss_mask, lm_labels, padding_mask


def forward_step(data_iterator, model, args, timers):
    """Forward step."""

    # Get the batch.
    timers('batch generator').start()
    tokens, types, next_sentence, loss_mask, lm_labels, padding_mask \
        = get_batch(data_iterator, timers)
    timers('batch generator').stop()

    # Forward model.
    lm_logits, nsp_logits = model(tokens, 1-padding_mask, tokentype_ids=types)

    nsp_loss = F.cross_entropy(nsp_logits.view(-1, 2).contiguous().float(),
                               next_sentence.view(-1).contiguous(),
                               ignore_index=-1)

    lm_loss_ = mpu.vocab_parallel_cross_entropy(lm_logits.contiguous().float(),
                                                lm_labels.contiguous())
    lm_loss = torch.sum(
        lm_loss_.view(-1) * loss_mask.reshape(-1)) / loss_mask.sum()

    loss = lm_loss + nsp_loss

    reduced_losses = torch.cat((lm_loss.clone().detach().view(1),
                                nsp_loss.clone().detach().view(1)))
    torch.distributed.all_reduce(reduced_losses)
    reduced_losses = reduced_losses / torch.distributed.get_world_size()
    lm_loss_reduced = reduced_losses[0]
    nsp_loss_reduced = reduced_losses[1]

    return loss, {'lm loss': lm_loss_reduced, 'nsp loss': nsp_loss_reduced}


def get_train_val_test_data(args):
    """Load the data on rank zero and boradcast number of tokens to all GPUS."""

    (train_data, val_data, test_data) = (None, None, None)

    # Data loader only on rank 0 of each model parallel group.
    if mpu.get_model_parallel_rank() == 0:
        data_config = configure_data()
        ds_type = 'BERT'
        data_config.set_defaults(data_set_type=ds_type, transpose=False)
        (train_data, val_data, test_data), tokenizer = data_config.apply(args)
        num_tokens = vocab_size_with_padding(tokenizer.num_tokens, args)
        # Need to broadcast num_tokens and num_type_tokens.
        token_counts = torch.cuda.LongTensor([num_tokens,
                                              tokenizer.num_type_tokens,
                                              int(args.do_train),
                                              int(args.do_valid),
                                              int(args.do_test)])
    else:
        token_counts = torch.cuda.LongTensor([0, 0, 0, 0, 0])

    # Broadcast num tokens.
    torch.distributed.broadcast(token_counts,
                                mpu.get_model_parallel_src_rank(),
                                group=mpu.get_model_parallel_group())
    num_tokens = token_counts[0].item()
    num_type_tokens = token_counts[1].item()
    args.do_train = token_counts[2].item()
    args.do_valid = token_counts[3].item()
    args.do_test = token_counts[4].item()

    args.vocab_size = num_tokens
    args.tokentype_size = num_type_tokens

    return train_data, val_data, test_data


if __name__ == "__main__":

    run('Pretrain BERT model', get_train_val_test_data,
        model_provider, forward_step)